Rutile titanium dioxide microspheres and ordered botryoidal shapes of same

ABSTRACT

Rutile TiO 2  microspheres and microparticles in a botryoidal morphology which form from ordered acicular aggregates of elongated TiO 2  crystallites that resemble nano-sized flower bouquets and/or triangular funnels, and process for their preparation by thermally hydrolyzing a soluble TiO 2  precursor compound in aqueous solution in the presence of a morphology controlling agent selected from carboxylic acids and amino acids.

CROSS-REFERENCE TO RELATED APPLICATIONS/INCORPORATION BY REFERENCESTATEMENT

The present application is a Divisional of U.S. application Ser. No.13/842,608, filed Mar. 15, 2013. The entirety of which is herebyexpressly incorporated herein by reference.

BACKGROUND OF THE INVENTION

The presently described and claimed inventive concept(s) relates to anovel chemical structure comprising rutile titanium dioxide (TiO₂)microspheres which are formed by aggregation of funnel-shaped rutilenanoparticles in which the broader dimension of the funnels assembleduring hydrolysis to become the outer surface of the microspheres. Moreparticularly, ordered aggregates of such microspheres further aggregateto resemble a larger botryoidal morphology.

Titanium dioxide (TiO₂) is known as a typical solid compound havingphotocatalytic activity and having utility in electronic, photovoltaicand photonic applications. Rutile and anatase crystal forms are known asmajor crystal forms of TiO₂ which display higher chemical stability andlarger refractive indices than those of amorphous TiO₂. It has also beenrecognized that TiO₂ particles having a high degree of crystallinity canexhibit a desirable level of photocatalytic activity.

U.S. Patent Publication No. 2012/0132515, for example, describes rutileTiO₂ nanoparticles wherein each has an exposed crystal face, making thenanoparticles useful as a photocatalyst and oxidation catalyst. The TiO₂nanoparticles are produced by subjecting a titanium compound to ahydrothermal treatment in an aqueous medium in the presence of ahydrophilic polymer, which is polyvinylpyrrolidone. The titaniumcompound, when hydrothermally treated in an aqueous medium, generallygives a rod-like crystal of rutile titanium dioxide having (110) and(111) faces. However, when hydrothermally treated in an aqueous mediumin the presence of polyvinylpyrrolidone, the rod-like crystal whichresults exhibits a novel exposed crystal face (001). It is noted thatthe hydrophilic polymer acts as a steric stabilizer or capping agent tothereby prevent aggregation of the rod-like crystals of rutile titaniumdioxide.

The need exists for improved methods for producing novel types of rutiletitanium dioxide (TiO₂) nano- and microparticles which have high surfaceareas, e.g., in the range of from 120 m²/g to 160 m²/g, and highrefractive indices for improved UV blocking capability and whichdemonstrate high performance levels in catalysis, e.g., biomassconversion, and in electronic applications, such as lithium ionbatteries and fuel cells.

SUMMARY OF THE INVENTION

The described and claimed inventive concepts(s) comprise, in oneembodiment, a method for preparing a novel form of rutile TiO₂nanoparticles which are ordered acicular aggregates of elongated TiO₂crystallites. The elongated TiO₂ crystallites are rod-like, e.g.,slender and/or needle-like, having a thickness of from 3 nm to 5 nm anda length which can vary from 20 nm up to 50 nm, although longer andshorter lengths may also be present. However, the elongated TiO₂crystallites assemble together during the process in a manner whichresults in ordered acicular aggregates that resemble nano-sized flowerbouquets or triangular funnels. By controlling the hydrolysis conditionsaccording to the inventive concept(s) described herein, the nano-sizedflower bouquets or triangular funnel-shaped nanoparticles furtheraggregate into somewhat larger spherical structures, i.e., microspheres,having a diameter of from 1 to 2 microns. The particles aggregate insuch a manner that the broader ends of the funnel-shaped particlesbecome the outer surfaces of the microspheres where the tips of thefunnels join, i.e., become assembled together, at the center of themicrospheres.

The method for preparing the microspheres comprises:

(a) forming an aqueous solution of a soluble titanium compound at atitanium concentration of from 0.5 to 1.0 moles per liter;

(b) introducing a morphology controlling agent selected from anα-hydroxy carboxylic acid of the formula R—CH(OH)COOH, an α-hydroxycarboxamide of the formula R—CH(OH)CONH₂ or an α-amino acid of theformula R—CH(NH₂)COOH, wherein R is an alkane, alkene, alkyne, arene, orcycloalkane group having 4 or fewer carbon atoms, into the solution atan acid- or carboxamide-to-titanium molar ratio of from 0.02 to 0.2while simultaneously heating the solution to a temperature in the rangeof from 75° C. to 80° C. with constant stirring;

(c) maintaining the stirred solution at a temperature in the range offrom 75° C. to 80° C. for a period of from one to 3 hours;

(d) elevating the temperature of the stirred solution to a value of from100° C. to the refluxing temperature and maintaining said temperaturefor a period of from 2 hours to 4 hours to form a reaction product;

(e) optionally neutralizing the reaction mixture which results from step(e);

(f) cooling the reaction mixture to room or ambient temperature; and

(h) separating and drying the reaction product.

The reaction product can then be calcined. Calcining, which can beadjusted over a wide range for time and temperature, operates to enhancethe properties of the resulting nanoparticles by expanding or openingthe pore structure and/or increasing the refractive index.

The morphology controlling agent is selected from lactic acid(CH₃CH(OH)COOH); 2-hydroxybutyric acid (C₂H₅CH(OH)COOH);2-hydroxypentanoic acid (C₃H₇CH(OH)COOH); 2-Hydroxyhexanoic acid(C₄H₉CH(OH)COOH); 2-Hydroxyisocaproic acid (CH₃CH(CH₃)CH₂CH(OH)COOH);alanine (CH₃CH(NH₂)COOH); valine (CH₃CH(CH₃)CH(NH₂)COOH); norvaline(C₃H₇CH(NH₂)COOH); isoleucine (C₂H₅CH(CH₃)CH(NH₂)COOH); leucine(CH₃CH(CH₃)CH₂CH(NH₂)COOH); and norleucine (C₄H₉CH(NH₂)COOH) andmixtures thereof.

The soluble titanium compound is selected from titanium oxychloride(TiOCl₂), titanium oxybromide (TiOBr₂), titanium oxyiodide (TiOI₂),titanium oxynitrate (TiO(NO₃)₂), titanium trichloride (TiCl₃), titaniumtribromide(TiBr₃), titanium oxalate (Ti₂(C₂O₄)₃), potassiumhexafluorotitanate(K₂TiF₆), ammonium hexafluorotitanate ((NH₄)₂TiF₆),potassium titanyloxolate (K₂TiO(C₂O₄)₂), ammonium titanyloxolate((NH₄)₂TiO(C₂O₄)₂), titanium bis(ammonium lactate) dihydroxide([CH₃CH(O)COONH₄]₂Ti(OH)₂) and mixtures thereof.

According to another embodiment, the described and claimed inventiveconcept(s) relates to a method for preparing rutile TiO₂ particles whichcomprise structures in a botryoidal morphology having a size in therange of from 10 to 20 microns. The botryoidal structures, also beingaggregates of elongated TiO₂ crystallites having a thickness of from 3nm to 5 nm, are formed by introducing TiO₂ seeds into the stirredsolution at a seed-to-TiO₂ molar ratio of from 0.0005 to 0.0015following introduction of the morphology controlling agent. The stirredsolution is then maintained at a temperature in the range of from 75° C.to 80° C. for a period of from one to 3 hours, and the process isfurther carried out as described above.

The described and claimed inventive concept(s) include, in otherembodiments, the microspheres and the botryoidal particles produced bythe described processes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an SEM (Scanning Electron Microscopy) image (9500magnification) of spherical-shaped rutile TiO₂ microparticles accordingto the invention.

FIG. 2 is an enlarged SEM image (50,000 magnification) which illustratesin more detail the spherical-shaped rutile TiO₂ microparticles accordingto the invention.

FIG. 3 is an SEM image (10,000 magnification) which illustratesspherical- shaped rutile TiO₂ microparticles arranged in structureswhich resemble a botryoidal morphology according to the invention.

FIG. 4 is an enlarged SEM image (50,000 magnification) which illustratesthe botryoidal morphology according to the invention in more detail.

FIGS. 5 and 6 are SEM images of rutile TiO₂ microparticles prepared bythermal hydrolydsis according to Example 3, but without benefit of amorphology controlling agent.

DETAILED DESCRIPTION OF THE INVENTION

The described and claimed inventive concepts(s) comprise, in oneembodiment, a method for preparing a novel form of rutile TiO₂nanoparticles which are ordered acicular aggregates of elongated TiO₂crystallites. The elongated TiO₂ crystallites are rod-like and have athickness of from 3 nm to 5 nm and a length which can vary generallyfrom 20 nm up to 50 nm. However, the elongated TiO₂ crystallitesassemble together during the process in a manner which results inordered acicular aggregates that resemble nano-sized flower bouquets ortriangular funnels. By controlling the hydrolysis conditions accordingto the inventive concept(s) described and claimed herein, the nano-sizedflower bouquets or triangular funnel-shaped nanoparticles furtheraggregate into somewhat larger spherical structures, i.e., microspheres,having a diameter of from 1 to 2 microns. Detailed examination under anelectron microscope confirms that the microspheres are indeed formed byaggregation of the funnel-shaped nanoparticles. The microspheres can beseen in FIGS. 1 and 2. The hydrolysis conditions are controlled in sucha manner that the nanoparticles aggregate so that the broader ends ofthe funnel-shaped particles become the outer surfaces of themicrospheres, and the tips of the funnels join, i.e., assemble together,at the center of the microspheres. The structure observed for themicrospheres indicates a large number of rutile nano-rods with variouslengths radiating outwardly from the center of the spherical structureswith each of the rods aligning at an angle normal to the surface of thespheres.

The novel rutile TiO₂ microspheres are prepared by thermally hydrolyzinga soluble TiO₂ precursor compound, or a mixture of such compounds, inaqueous solution in the presence of a morphology controlling agent, or amixture of morphology controlling agents, under specific conditions. Theprocess is a wet chemical hydrolysis method in which the structure ofthe microspheres is controlled by controlling the structure of thenano-sized flower bouquets or triangular funnel-shaped nanoparticles. Amorphology controlling agent, or a mixture of morphology controllingagents, is used that is selected from (i) an α-hydroxy carboxylic acidof the formula R—CH(OH)COOH, (ii) an α-hydroxy carboxamide of theformula R—CH(OH)CONH₂, or (iii) an α-amino acid of the formulaR—CH(NH₂)COOH, wherein R is an alkane, alkene, alkyne, arene, orcycloalkane group having 4 or fewer carbon atoms.

The process begins by forming an aqueous solution of a soluble titaniumcompound at a titanium concentration of from 0.1 to 1.5 moles per liter,but preferably 0.5 to 1.0 moles per liter, optionally in the presence ofa mineral acid. Distilled or deionized water can be used to form theaqueous solution, and a mineral acid, e.g., hydrochloric acid (HCl), canbe introduced as needed for controlling the rate of hydrolysis.

The morphology controlling agent, or a mixture thereof, is introducedinto the solution at an acid- or carboxamide-to-titanium molar ratio offrom 0.02 to 0.4, although best results have been observed when theratio is from 0.02 to 0.2. The solution is simultaneously heated to atemperature in the range of from 75° C. to 80° C. with constantstirring.

The temperature of the stirred solution is next elevated to a value offrom 100° C. to the refluxing temperature and maintained at that levelfor a period of from 2 hours to 4 hours during which time a reactionproduct is formed. The solution, i.e., reaction mixture, is then cooledto room or ambient temperature, and, optionally, it can be neutralized,e.g., pH of 5 to 8, with introduction of a base, such as an ammoniasolution or a sodium hydroxide solution. The reaction product is thenseparated by filtration and washed with dionized water to remove saltsgenerated during hydrolysis. The resulting filter cake can then be driedin an oven or re-slurried with water and spray dried.

As noted above, the reaction product can then be calcined as desiredover a wide range of time and temperature to enhance the properties ofthe resulting nanoparticles, such as by expanding or opening the porestructure and/or increasing the refractive index.

For best results the soluble titanium precursor compound is selectedfrom titanium oxychloride (TiOCl₂), titanium oxybromide (TiOBr₂),titanium oxyiodide (TiOI₂), titanium oxynitrate (TiO(NO₃)₂), titaniumtrichloride (TiCl₃), titanium tribromide(TiBr₃), titanium oxalate(Ti₂(C₂O₄)₃), potassium hexafluorotitanate(K₂TiF₆), ammoniumhexafluorotitanate ((NH₄)₂TiF₆), potassium titanyloxolate(K₂TiO(C₂O₄)₂), ammonium titanyloxolate ((NH₄)₂TiO(C₂O₄)₂), and titaniumbis(ammonium lactate) dihydroxide ([CH₃CH(O)COONH₄]₂Ti(OH)₂). Othercommercially available soluble titanium precursor compounds can bedeployed in the process and produce satisfactory results and, althoughnot specifically named herein, they are embraced within the describedand claimed inventive concept(s).

As noted above, morphology controlling agents, or mixtures thereof, forcarrying out the inventive concept(s) include (i) α-hydroxy carboxylicacids of the formula R—CH(OH)COOH, (ii) α-hydroxy carboxamides of theformula R-—CH(OH)CONH₂, and (iii) α-amino acids of the formulaR—CH(NH₂)COOH, wherein R is an alkane, alkene, alkyne, arene, orcycloalkane group having 4 or fewer carbon atoms. Examples of suchmorphology controlling agents include, but are not limited to, lacticacid (CH₃CH(OH)COOH); 2-hydroxybutyric acid (C₂H₅CH(OH)COOH);2-hydroxypentanoic acid (C₃H₇CH(OH)COOH); 2-Hydroxyhexanoic acid(C₄H₉CH(OH)COOH); 2-Hydroxyisocaproic acid (CH₃CH(CH₃)CH₂CH(OH)COOH);alanine (CH₃CH(NH₂)COOH); valine (CH₃CH(CH₃)CH(NH₂)COOH); norvaline(C₃H₇CH(NH₂)COOH); isoleucine (C₂H₅CH(CH₃)CH(NH₂)COOH); leucine(CH₃CH(CH₃)CH₂CH(NH₂)COOH); and norleucine (C₄H₉CH(NH₂)COOH) andmixtures thereof.

It has also been discovered according to the inventive concept(s)described herein that the hydrolysis conditions can be further adjustedto produce even larger aggregates of about 10 to 20 microns in sizewhich exhibit a botryoidal morphology or texture. A botryoidal textureis one in which the particle has a globular external form resembling,for example, a bunch of grapes. The botryoidal structures, also beingaggregates of the elongated TiO₂ crystallites, form when TiO₂ seeds areintroduced into the stirred solution at a seed-to-TiO₂ molar ratio offrom 0.0005 to 0.0015 following introduction of the morphologycontrolling agent. The stirred solution is then maintained at atemperature in the range of from 75° C. to 80° C. for a period of fromone to 3 hours, and the process is further carried out as describedabove. The rutile TiO₂ microspheres and the botryoidal particles becomedenser and their pore volumes become lower in comparison with thefunnel-shaped triangular nanoparticles, although the powder specificsurface areas for the particle varieties are similar to one another,i.e., in the range from 120 m²/g to 160 m²/g. Typical pore volumes forthe microspheres and botryoidal particles are in the range of from 0.1cm³/g-0.3 cm³/g.

EXAMPLES

The present invention will be illustrated in further detail withreference to the working examples which follow and FIGS. 1-8. It shouldbe noted, however, that these examples should not be construed to limitthe scope of the described and claimed inventive concept(s).

Example 1 Preparation of TiO₂ Microspheres Using Carboxylic Acids

1,255 g of deionized water, 6.6 g lactic acid (85% solution from AlfaAesar), 97 g HCl solution (37% from Fisher Scientific), and 397 g oftitanium oxychloride solution (25.2% in TiO₂, from Millennium InorganicChemicals) were mixed together in a heated reactor equipped with a glasscondenser and an overhead stirrer. While being constantly stirred, themixture was heated to 75° C., and the hydrolysis reaction was maintainedat 75° C. for 2 hours. The reaction temperature was then increased to103° C., and that temperature was maintained for 4 hours. The hydrolysiswas essentially complete at this stage.

The resulting reaction mixture was then cooled to room temperature andtransferred to a different container where the particles formed wereallowed to settle for a few hours. After essentially all of theparticles were observed to have settled to the bottom of the container,the mother liquor, i.e., liquid reaction medium, was removed and aboutthe same volume of fresh deionized water was added to the container. Thereaction mixture was then stirred to re-slurry the particles, and thenthe pH of the slurry was increased to a value of about 7 by slowaddition of an ammonia solution (˜29%, Fisher Scientific). The particlescomprising the reaction product were then separated from the liquidreaction mixture using a Buchner filter and washed with deionized wateruntil the conductivity of the filtrate was lowered to about 500 μS/cm.The wet filter cake sample was then stored as a slurry by re-slurringthe filter cake with a small amount of deionized water. The powder formof the sample was obtained by drying the slurry sample in an ovenovernight at 90° C. X-ray Diffraction (XRD) measurement on the powdersample indicates that the sample contained 100% rutile with crystallitesize about 7.6 nm. BET measurement on the powder sample showed that thepowder had a specific surface area of 122 m²/g and a pore volume of 0.1cm³/g.

SEM images of the slurry sample are shown in FIG. 1 at a magnificationof 9,500 where the spherical microspheres can be observed. Enlargedmicrospheres can be seen more clearly in FIG. 2 at a magnification of50,000.

The TiO₂ microspheres shown in FIGS. 1 and 2 can be calcined, which canbe adjusted for time and temperature, to enhance the properties of theresulting microparticles by expanding or opening the pore structureand/or increasing the refractive index.

Example 2 Preparation of Botryoidal Micro-Particles Using Carboxylic

The same procedure was followed as was followed in Example 1, exceptthat 13.2 g of lactic acid (85% solution from Alfa Aesar) was added. Inaddition, the final hydrolysis temperature was maintained at 95° C. for4 hours instead of 103° C. SEM images of the sample are shown in FIG. 3at a magnification of 10,000. A botryoidal texture can be observed inwhich the particle has a globular external form resembling, for example,a bunch of grapes. FIG. 4 shows an enlarged SEM image (b 50,000magnification) which illustrates the botryoidal morphology in moredetail.

XRD measurement of the sample confirmed that the sample contained 100%rutile TiO₂ with a crystallite size of 7.8 nm. BET measurement showed aspecific area of 161 m²/g and a pore volume of 0.12 cm³/g.

Comparative Example 3 Hydrolysis without a Morphology ControllingAgent(s)

The same procedure was followed as was followed for Example 1, exceptthat no organic acids (morphology controlling agent) were added duringthe procedure. SEM images of the sample can be seen in FIGS. 5 and 6.XRD measurement showed that the sample contained 100% rutile TiO₂,however, the SEM images show clearly that the sample prepared by thermalhydrolysis without a morphology controlling agent has a differentmorphology than the microsphere and botryoidal particle samples shown inFIGS. 1-4 in which a morphology controlling agent was used.

1-7. (canceled)
 8. Rutile TiO₂ microparticles which comprise generallyspherical structures in the range of from 1 to 2 microns in diameter,said spherical structures comprising ordered acicular aggregates ofelongated TiO₂ crystallites having a thickness in the range of from 3 nmto 5 nm in which one end of each of said elongated TiO₂ crystallites arejoined into a cluster such that the opposite ends of each of saidelongated TiO₂ crystallites extend outwardly and terminate at an anglenormal to the outer surface forming said spherical structure.
 9. RutileTiO₂ microparticles which comprise generally spherical structures in therange of from 1 to 2 microns in diameter, said spherical structurescomprising ordered acicular aggregates of elongated TiO₂ crystallites,produced by the process comprising: (a) forming an aqueous solution of asoluble titanium compound at a titanium concentration of from 0.5 to 1.0moles per liter; (b) introducing a morphology controlling agent selectedfrom the group consisting of an α-hydroxy carboxylic acid of the formulaR—CH(OH)COOH, an α-hydroxy carboxamide of the formula R—CH(OH)CONH₂ oran α-amino acid of the formula R—CH(NH₂)COOH, wherein R is an alkane,alkene, alkyne, arene, or cycloalkane group having 4 or fewer carbonatoms, into the solution at an acid- or carboxamide-to-titanium molarratio of from 0.02 to 0.2 while simultaneously heating the solution to atemperature in the range of from 75° C. to 80° C. with constantstirring; (c) maintaining the stirred solution at a temperature in therange of from 75° C. to 80° C. for a period of from one to 3 hours; (d)elevating the temperature of the stirred solution to a value of from100° C. to the refluxing temperature and maintaining said temperaturefor a period of from 2 hours to 4 hours to form a reaction product; (e)optionally neutralizing the reaction mixture which results from step(e); (f) cooling the reaction mixture to room or ambient temperature;and (h) separating and drying the reaction product.
 10. The rutile TiO₂microparticles of claim 9 wherein said elongated TiO₂ crystallites havea length of from 20 nm to 50 nm and a thickness of from 3 nm to 5 nm.11. The rutile TiO₂ microparticles of claim 10 wherein one of the endsfrom each of said elongated TiO₂ crystallites assemble into a clusterwhereby the opposite ends of each of said crystallites extend outwardlyand terminate at an angle normal to the outer surface forming saidspherical structure.
 12. The rutile TiO₂ microparticles of claim 9wherein said morphology controlling agent is selected from lactic acid(CH₃CH(OH)COOH); 2-hydroxybutyric acid (C₂H₅CH(OH)COOH);2-hydroxypentanoic acid (C₃H₇CH(OH)COOH); 2-Hydroxyhexanoic acid(C₄H₉CH(OH)COOH); 2-Hydroxyisocaproic acid (CH₃CH(CH₃)CH₂CH(OH)COOH);alanine (CH₃CH(NH₂)COOH); valine (CH₃CH(CH₃)CH(NH₂)COOH); norvaline(C₃H₇CH(NH₂)COOH); isoleucine (C₂H₅CH(CH₃)CH(NH₂)COOH); leucine(CH₃CH(CH₃)CH₂CH(NH₂)COOH); and norleucine (C₄H₉CH(NH₂)COOH) andmixtures thereof.
 13. The rutile TiO₂ microparticles of claim 9 whereinsaid soluble titanium compound is selected from titanium oxychloride(TiOCl₂), titanium oxybromide (TiOBr₂), titanium oxyiodide (TiOI₂),titanium oxynitrate (TiO(NO₃)₂), titanium trichloride (TiCl₃), titaniumtribromide(TiBr₃), titanium oxalate (Ti₂(C₂O₄)₃), potassiumhexafluorotitanate(K₂TiF₆), ammonium hexafluorotitanate ((NH₄)₂TiF₆),potassium titanyloxolate (K₂TiO(C₂O₄)₂), ammonium titanyloxolate((NH₄)₂TiO(C₂O₄)₂), titanium bis(ammonium lactate) dihydroxide([CH₃CH(O)COONH₄]₂Ti(OH)₂) and mixtures thereof.
 14. The rutile TiO₂microparticles of claim 12 wherein said soluble titanium compound isselected from titanium oxychloride (TiOCl₂), titanium oxybromide(TiOBr₂), titanium oxyiodide (TiOI₂), titanium oxynitrate (TiO(NO₃)₂),titanium trichloride (TiCl₃), titanium tribromide(TiBr₃), titaniumoxalate (Ti₂(C₂O₄)₃), potassium hexafluorotitanate(K₂TiF₆), ammoniumhexafluorotitanate ((NH₄)₂TIF₆), potassium titanyloxolate(K₂TiO(C₂O₄)₂), ammonium titanyloxolate ((NH₄)₂TiO(C₂O₄)₂), titaniumbis(ammonium lactate) dihydroxide ([CH₃CH(O)COONH₄]₂Ti(OH)₂) andmixtures thereof.
 15. The rutile TiO₂ microparticles of claim 14 whereinsaid morphology controlling agent is lactic acid (CH₃CH(OH)COOH), andsaid soluble titanium compound is titanium oxychloride (TiOCl₂).
 16. Amethod for preparing rutile TiO₂ particles which comprise structures ina botryoidal morphology having a size in the range of from 10 to 20microns, said structures being aggregates of elongated TiO₂ crystalliteshaving a thickness of from 3 nm to 5 nm, said method comprising: (a)forming an aqueous solution of a soluble titanium compound at a titaniumconcentration of from 0.5 to 1.0 moles per liter; (b) introducing amorphology controlling agent selected from an α-hydroxy carboxylic acidof the formula R—CH(OH)COOH, an a-hydroxy carboxamide of the formulaR—CH(OH)CONH₂ or an a-amino acid of the formula R—CH(NH₂)COOH, wherein Ris an alkane, alkene, alkyne, arene, or cycloalkane group having 4 orfewer carbon atoms, into the solution at an acid- orcarboxamide-to-titanium molar ratio of from 0.02 to 0.2 whilesimultaneously heating the solution to a temperature in the range offrom 75° C. to 80° C. with constant stirring; (c) introducing TiO₂ seedsinto the stirred solution at a seed-to-TiO₂ molar ratio of from 0.0005to 0.0015 and maintaining the stirred solution at a temperature in therange of from 75° C. to 80° C. for a period of from one to 3 hours; (d)elevating the temperature of the stirred solution to a value of from100° C. to the refluxing temperature and maintaining said temperaturefor a period of from 2 hours to 4 hours to form a reaction product; (e)optionally neutralizing the reaction mixture resulting from step (d);(f) cooling the reaction mixture to room or ambient temperature; and (g)separating and drying the reaction product.
 17. The method of claim 16wherein said morphology controlling agent is selected from lactic acid(CH₃CH(OH)COOH); 2-hydroxybutyric acid (C₂H₅CH(OH)COOH);2-hydroxypentanoic acid (C₃H₇CH(OH)COOH); 2-Hydroxyhexanoic acid(C₄H₉CH(OH)COOH); 2-Hydroxyisocaproic acid (CH₃CH(CH₃)CH₂CH(OH)COOH);alanine (CH₃CH(NH₂)COOH); valine (CH₃CH(CH₃)CH(NH₂)COOH); norvaline(C₃H₇CH(NH₂)COOH); isoleucine (C₂H₅CH(CH₃)CH(NH₂)COOH); leucine(CH₃CH(CH₃)CH₂CH(NH₂)COOH); and norleucine (C₄H₉CH(NH₂)COOH) andmixtures thereof.
 18. The method of claim 16 wherein said solubletitanium compound is selected from titanium oxychloride (TiOCl₂),titanium oxybromide (TiOBr₂), titanium oxyiodide (TiOI₂), titaniumoxynitrate (TiO(NO₃)₂), titanium trichloride (TiCl₃), titaniumtribromide(TiBr₃), titanium oxalate (Ti₂(C₂O₄)₃), potassiumhexafluorotitanate(K₂TiF₆), ammonium hexafluorotitanate ((NH₄)₂TiF₆),potassium titanyloxolate (K₂TiO(C₂O₄)₂), ammonium titanyloxolate((NH₄)₂TiO(C₂O₄)₂), titanium bis(ammonium lactate) dihydroxide([CH₃CH(O)COONH₄]₂Ti(OH)₂) and mixtures thereof.
 19. The method of claim17 wherein said soluble titanium compound is selected from titaniumoxychloride (TiOCl₂), titanium oxybromide (TiOBr₂), titanium oxyiodide(TiOI₂), titanium oxynitrate (TiO(NO₃)₂), titanium trichloride (TiCl₃),titanium tribromide(TiBr₃), titanium oxalate (Ti₂(C₂O₄)₃), potassiumhexafluorotitanate(K₂TiF₆), ammonium hexafluorotitanate ((NH₄)₂TiF₆),potassium titanyloxolate (K₂TiO(C₂O₄)₂), ammonium titanyloxolate((NH₄)₂TiO(C₂O₄)₂), titanium bis(ammonium lactate) dihydroxide([CH₃CH(O)COONH₄]₂Ti(OH)₂) and mixtures thereof.
 20. The method of claim19 wherein said morphology controlling agent is lactic acid(CH₃CH(OH)COOH), and said soluble titanium compound is titaniumoxychloride (TiOCl₂).
 21. Rutile TiO₂ microparticles comprisingstructures in a botryoidal morphology having a size in the range of from10 to 20 microns and formed by the process of: (a) forming an aqueoussolution of a soluble titanium compound at a titanium concentration offrom 0.5 to 1.0 moles per liter; (b) introducing a morphologycontrolling agent selected from an α-hydroxy carboxylic acid of theformula R—CH(OH)COOH, an α-hydroxy carboxamide of the formulaR—CH(OH)CONH₂ or an α-amino acid of the formula R—CH(NH₂)COOH, wherein Ris an alkane, alkene, alkyne, arene, or cycloalkane group having 4 orfewer carbon atoms, into the solution at an acid- orcarboxamide-to-titanium molar ratio of from 0.02 to 0.2 whilesimultaneously heating the solution to a temperature in the range offrom 70° C. to 80° C. with constant stirring; (c) introducing TiO₂ seedsinto the stirred solution at a seed-to-TiO₂ molar ratio of from 0.0005to 0.0015 and maintaining the stirred solution at a temperature in therange of from 70° C. to 80° C. for a period of from one to 3 hours; (d)maintaining the stirred solution at a temperature in the range of from70° C. to 80° C. for a period of from one to 3 hours; (e) elevating thetemperature of the stirred solution to a value of from 100° C. to therefluxing temperature and maintaining said temperature for a period offrom 2 hours to 4 hours to form a reaction product; (f) optionallyneutralizing the reaction mixture resulting from step (e); (g) coolingthe reaction mixture to room or ambient temperature and separating anddrying the reaction product.
 22. The rutile TiO₂ microparticles of claim21 wherein: (a) said morphology controlling agent is selected fromlactic acid (CH₃CH(OH)COOH); 2-hydroxybutyric acid (C₂H₅CH(OH)COOH);2-hydroxypentanoic acid (C₃H₇CH(OH)COOH); 2-Hydroxyhexanoic acid(C₄H₉CH(OH)COOH); 2-Hydroxyisocaproic acid (CH₃CH(CH₃)CH₂CH(OH)COOH);alanine (CH₃CH(NH₂)COOH); valine (CH₃CH(CH₃)CH(NH₂)COOH); norvaline(C₃H₇CH(NH₂)COOH); isoleucine (C₂H₅CH(CH₃)CH(NH₂)COOH); leucine(CH₃CH(CH₃)CH₂CH(NH₂)COOH); and norleucine (C₄H₉CH(NH₂)COOH) andmixtures thereof, and (b) said soluble titanium compound is selectedfrom titanium oxychloride (TiOCl₂), titanium oxybromide (TiOBr₂),titanium oxyiodide (TiOI₂), titanium oxynitrate (TiO(NO₃)₂), titaniumtrichloride (TiCl₃), titanium tribromide(TiBr₃), titanium oxalate(Ti₂(C₂O₄)₃), potassium hexafluorotitanate(K₂TiF₆), ammoniumhexafluorotitanate ((NH₄)₂TiF₆), potassium titanyloxolate(K₂TiO(C₂O₄)₂), ammonium titanyloxolate ((NH₄)₂TiO(C₂O₄)₂), titaniumbis(ammonium lactate) dihydroxide ([CH₃CH(O)COONH₄]₂Ti(OH)₂) andmixtures thereof.
 23. Rutile TiO₂ microparticles in a botryoidalmorphology having a size in the range of from 10 to 20 microns whichcomprise an assembly of generally spherical structures in the range offrom 1 to 2 microns in diameter, said spherical structures comprisingordered acicular aggregates of elongated TiO₂ crystallites having athickness in the range of from 3 nm to 5 nm in which one end of each ofsaid elongated TiO₂ crystallites are joined into a cluster such that theopposite ends of each of said elongated TiO₂ crystallites extendoutwardly and terminate at an angle normal to the outer surface formingsaid spherical structure.